This invention pertains to alkaline batteries, and, in particular, to separators for use in such batteries.
Separators developed specifically for alkaline batteries are known in the prior art. Such separators are used to electrically insulate the negative and positive battery electrodes so that the battery electrolyte forms the only ionically conducting path therebetween. In order for the separators to provide this insulating function, the separators must exhibit a low electrical resistance, must be chemically stable in the electrolyte environment, must resist stiffening and cracking, must be wettable to the battery electrolyte, and must limit active material transport.
U.S. Pat. No. 3,351,495 discloses a class of prior art separators having composition intended to realize such characteristics. In these separators plasticizers and filler materials are incorporated in a polyolefin (e.g., polyethelene, polypropylene) and portions thereof leached out prior to battery formation to provide a resultant separator having a microporous structure. Such microporous structure is said to prevent solid electrode active material from passing through the separator and to further inhibit passage of positive electrode ions to the negative electrode.
U.S. patent application Ser. No. 923,216 assigned to the same assignee hereof discloses a separator wherein a thermoplastic contituent (e.g., polysulfone, polypropylene, nylon) is provided with a filler material which is reactant with alkaline electrolyte of the battery and, therefore, is leachable in situ during battery construction. The resultant separator of this application is of microporous structure sufficient to prevent dendritic growth and provide desired electrode ion diffusion. This application also discloses the incorporation of plasticizers and wetting agents in the thermoplastic-reactive material composition to provide additional enhanced separator properties.
It is an object of the present invention to provide an improved separator for alkaline batteries employing electrodes of zinc active material.
It is a further object of the present invention to provide a separator of the last-mentioned type having improved resistance to zinc ion diffusion.